The invention generally relates to removing noise from seismic data that is obtained from towed seismic sensors.
Seismic exploration involves surveying subterranean geological formations for hydrocarbon deposits. A survey typically involves deploying seismic source(s) and seismic sensors at predetermined locations. The sources generate seismic waves which propagate into the geological formations creating pressure changes and vibrations along their way. Changes in elastic properties of the geological formation scatter the seismic waves, changing their direction of propagation and other properties. Part of the energy emitted by the sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes (hydrophones), others to particle motion (geophones), and industrial surveys may deploy only one type of sensors or both. In response to the detected seismic events, the sensors generate electrical signals to produce seismic data. Analysis of the seismic data can then indicate the presence or absence of probable locations of hydrocarbon deposits.
Some surveys are known as “marine” surveys because they are conducted in marine environments. However, “marine” surveys may be conducted not only in saltwater environments, but also in fresh and brackish waters. In one type of marine survey, called a “towed-array” survey, an array of seismic sensor-containing streamers and sources is towed behind a survey vessel.
The data that is recorded from the towed streamers may be contaminated with vibration noise. The vibration noise typically has a relatively slow apparent velocity along the streamer, and spatial aliasing of the vibration noise inside the signal cone may be reduced or avoided by increasing the density (and number) of the sensors along the streamer. However, it may be impractical and/or relatively costly to reduce the vibration noise to the desired level by merely increasing the number of sensors.